The invention relates to an over-center hinge for cabinet doors which has a door-related part in the form of a cup designed for installation in a mortise, in which are pivotingly mounted the ends of two hinge links whose other ends are mounted on the supporting-wall-related part in the form of a supporting arm thereby creating a four-pivot linkage. A pressure piece biased by a spring is pivoted within the supporting arm on the inner hinge link nearer to the supporting wall and bears against a surface which undergoes a change of position relative to the pressure piece upon the movement of the hinge, such that the hinge is resiliently urged into the closed position upon passing over a dead center in the closing movement.
Over-center hinges, in which the over-center mechanism is situated substantially out of sight in the interior of the supporting arm, are known, the configuration being such, for example, that the pressure piece is a roller mounted on a spring-biased lever or bridle pivoted in the support arm and cooperates with a surface formed on or attached to one of the links (German AS No. 1,708,227, U.S. Pat. No. 3,590,420). In addition to the relatively great complexity of design of these hinges and the consequently high cost of their manufacture, space availability problems are encountered. This is because the interior of the supporting arm of such a hinge must be kept largely free to accommodate the fastening and adjustment means whereby provision is made for fastening the supporting arm to the mounting plate provided on the supporting wall of the cabinet and for the necessary adjustment or alignment of the hinge. In the known hinges, this space is diminished by the bridle holding the pressure roller and by the spring. In an over-center hinge of the kind mentioned in the beginning (German OS No. 2,516,084), the attempt has therefore been made to shift the over-center mechanism toward the forward supporting arm end facing the door-related part of the hinge, in order thus to obtain more space for the fastening and adjusting means within the supporting arm. The over-center mechanism is formed by a plastic pressure piece pivotingly attached in the middle portion of the inner hinge link with its free end pointing toward the interior of the supporting arm; this pressure piece is biased by a helical spring bearing against the pressure piece at one end and against the pivot pin in the eye of the supporting-wall end of the inner link at the other, thereby urging a projection on the supporting-arm end of the pressure piece against the inner surface of the transverse wall of the upper supporting arm when the hinge is in the open state. When the hinge swings from the open to the closed position, the actual bearing surface of the pressure piece gradually approaches the eye at the supporting arm end of the outer hinge link. During the last portion of the closing movement, this bearing surface slides on the pivot eye, thereby slightly increasing the spring bias. Shortly before the closed position is reached, the bearing surface is then shaped such that the helical spring exerts a closing torque on the hinge, which draws the door mounted by the hinge resiliently to the closed position and holds it there. The known hinge is completely functional, but as far as the desired saving of space inside of the supporting arm is concerned it falls short of the optimum, because the pressure piece projection which in the area of the hinge-open position points to the interior of the supporting arm and bears against the supporting arm interferes with the provision of an adjusting screw in the area of the projection.